The invention relates to an antenna and more particularly to a gain-adjustable antenna.
The main function of antenna is to transform energy originally carried by a transmission line to the air by means of electromagnetic field and receives and transforms electromagnetic energy from the air to a transmission line.
Antennas are classified as directional or omni-directional depending on the direction of radiation. Some important antenna parameters include frequency range, pattern, VSWR and gain. Antenna gain may affect the transmission range. With the same transmission power and identical receiving amplifier, using high-gain antenna results in longer transmission distance. Antennas with higher gain achieve better communication quality. It is difficult, however, to provide a flexible antenna gain suitable for every environment, because antenna gain is typically a fixed value.